Young-Earth Creationists are catastrophists. Their
explanations involve a small number of rapid, global events, such as
the Flood.

The Scientist's Response

Uniformitarianism was started in 1795 by James Hutton's Theory
of the Earth. The idea was championed by later authors, such as
Charles Lyell, and basically what they meant was that the past should
be explained by processes which can be seen in the present day.

Some geologists of Lyell's school did indeed carry things too far,
and insist on only slow, gradual processes. The residue of
that, in the 1900's, was mostly the attitude that catastrophe
explanations should not be used until other explanations were ruled
out. But it's not worth arguing about the views of long-dead
scientists. The important point is what living ones say.

They know from recent history that volcanoes can make abrupt
changes to landscapes, and that a river flood can dump yards of mud in
the space of days. So, it is obvious that some rocks formed more
quickly than others. Lyell himself said so in 1830 in his
Principles of Geology.

In the last few decades, there has been much more appreciation of
this variability of rate. We now explain the scablands of Washington
by the sudden bursting of a huge glacial dam. It is now a common idea
that a meteorite killed off the dinosaurs. We also appreciate that
conditions were once different. For instance, the atmosphere of the
early earth had no free oxygen.

So, modern geology is not just about slow, gradual
processes. That said, it is clear that slow processes exist. For
instance, the Santa Barbara basin is today acquiring sediment at one
foot per century.

Physicists sometimes use the same word. When they use it, they mean
that reality is lawful - that there is some set of laws which
uniformly apply everywhere, and which have always applied.